Self supporting piastic bottle with textured thin walls

ABSTRACT

A plastic bottle, made of polyethylene (PE), polypropylene (PP), or poly(ethylene terephthalate) (PET), blown with a very thin overall wall thickness within the range 0.1 to 0.3 mm, includes a triangular or polygonal cross-section, the bottle being preferably surrounded by a supporting jacket. The bottle can be blown with a uniform wall thickness and adequate strength without the need for reinforcing ribs via walls formed by pressing them against the surface of a blow mold which has been worked at least in some areas by etching, form-cutting or eroding, having features with heights of 0.05 to 0.15 mm.

BACKGROUND

1. Field of the Invention

This invention relates to a generally thin-walled, blow-molded plasticbottles, and more particularly to such bottles typically surrounded by abottomless and topless supporting jacket of either polyethylene (PE),polypropylene (PP) or polyethylene terephthalate (PET) with a very thinoverall wall thickness of 0.1 to 0.3 mm

2. Discussion of Related Art

Known processes for the production of plastic bottles in blow molds,so-called bottle blowing processes, are also suitable for the productionof extremely thin-walled plastic bottles. Plastic bottles ofpolyethylene terephthalate (PET) are produced, for example, by initiallyinjection-molding a parison and then blow-molding the parison under theeffect of heat into the required bottle shape. Plastic bottles ofpolyethylene (PE) are produced, for example, by feeding a PE tube to theblow molds of bottle blowing machines and blow-molding the tube in theblow molds to form bottles. It is known that very thin-walled plasticbottles can be produced by these bottle blowing processes. These plasticbottles have a smooth surface texture. To increase the strength andstability of the bottles and to prevent them from bulging, particularlyduring and after filling with liquid, it is known (cf. EP-A-0 198 587)that the bottles can be provided with pronounced stabilizing andstiffening ribs and recesses. This requires particularly expensive andrelatively complicated blow molds. The need for a uniform and constantwall thickness over the entire extent of the bottle wall is a problemwhich has not been satisfactorily solved in these known bottles.

Very thin-walled blow-molded plastic bottles of polyethylene (PE) with awall thickness of 0.1 to 0.3 mm and a rectangular cross-sectionsurrounded by a bottomless and topless supporting jacket of cardboardare known from DE-A-39 21 258 and have been on the market for some time.The need for a uniform and constant wall thickness over the entireextent of the bottle wall is again a problem which has not beensatisfactorily solved in these bottles either. During blow molding inthe blow molds, extremely thin zones well below the required wallthickness are formed in the 0.1 to 0.3 mm thick bottle wall; in somecases, holes are even formed in the bottle wall. Another disadvantage ofthese thin-walled plastic bottles is that the side walls show signs ofbuckling on removal from the blow mold and bulge out when filled withliquid or free-flowing product.

In addition, it is generally known that plastic bottles with standardwall thicknesses of 0.35 to 0.8 mm can be produced in blow moldstoughened, for example, by etching or sandblasting if parts of the outersurface of the bottle are to have a matt or rough texture for reasons ofoptical design. However, this does not affect the stability or rigidityof the bottles on account of the relatively thick walls of the bottlesto which this process has hitherto been applied.

SUMMARY OF THE INVENTION

An object of the invention is to provide a very thin-walled plasticbottle free from stiffening ribs which can be produced by blow molding,has a uniform wall thickness, and has sufficient strength to resistbulging.

In a plastic bottle of the invention, are at least the side bottle wallsare formed by application to a blow molding surface at least locallyprepared by etching, profile milling or erosion for texturing the wallto depths of 0.05 to 0.15 mm.

Blow-molded plastic bottles with a total wall thickness of 0.1 to 0.3 mmtextured to depths of 0.05 to 0.15 mm in their walls are improved intheir overall stability and, in particular, in their resistance tobulging by comparison with smooth-surface plastic bottles having thesame wall thickness. It is sufficient in regard to improved resistanceto bulging if only the side walls of the plastic bottle are textured inaccordance with the invention. The texturing is achieved by preparingthe corresponding surfaces of the blow mold, to which those parts of theplastic material to be textured are applied during blow molding of theplastic bottle, by etching, profile milling or erosion in such a waythat the bottle is textured to depths of 0.05 to 0.15 mm in the appliedparts of the bottle wall. It has been found in this regard that it issufficient to prepare the blow molds in such a way that the preparedsurfaces are textured to depths of 0.01 to 0.03 mm. In view of the verythin overall wall thicknesses of 0.1 to 0.3 mm, the texture isreproduced both on the outer surface and on the inner surface of thecorresponding parts of the plastic bottle. In this way, the distancebetween the outer surface and the inner surface (overall wall thickness)in the textured parts of the bottle wall is increased by comparison withsmooth-walled plastic bottles having the same wall thickness of 0.1 to0.3 mm, without the actual wall thickness being increased or anincreased amount of plastic material being used. Those parts of thebottle wall textured to depths of 0.05 to 0.15 mm show improved andincreased stiffness in flexure. The thin-walled plastic bottlesaccording to the invention with overall wall thicknesses of 0.1 to 0.3mm locally textured to depths of 0.05 to 0.15 mm on their walls can beproduced in bottle blowing machines designed for standard thick-walledplastic bottles. To produce the thin-walled plastic bottles, the blowmolds used in the bottle blowing process have to be prepared by etching,profile milling or erosion, etching being understood to includephotoetching, graining, structuring or texturing. The plastic bottlesblow-molded in such blow molds have a constant and uniform wallthickness over the extent of their walls and high stability and strengthdespite their extremely low wall thickness and overall wall thicknessvalues. Compared with the smooth thin-walled plastic bottles known fromDE-A-39 21 258, they are distinctly improved in their stability andstrength and are distinguished by uniform wall thickness over theirwalls. In corners in particular, there are no longer any thin zones withundesirably low wall thickness values. The plastic bottles thus producedshow very high dimensional accuracy whereas untextured thin-walledbottles have a marked tendency to bulge, particularly over flatsurfaces, such as the side walls. They undergo negligible, i.e.unproblematical, bulging during and after filling with liquid orfree-flowing product. There is no longer any need for stiffening ribsand/or recesses. The production of thin-walled plastic bottles incorrespondingly prepared blow molds also affords advantages for thebottle blowing process. It has been found that textured blow moldsprovide for better mold venting at the faces and mold parting lines, forbetter cooling and for a shorter cycle time in the actual bottle blowingprocess. In addition, it has been found that plastic bottles textured todepths of 0.05 to 0.15 mm in parts of their walls can be transportedparticularly effectively on the conveyor belts of filling machines whenthe bottom wall is also correspondingly textured. Compared withsmooth-walled plastic bottles with the same wall thickness and henceequally light weight, the plastic bottle according to the invention isdistinguished by distinctly better slip and transport behavior onconveyor belts of filling machines.

It is sufficient, particularly in the case of plastic bottles surroundedby a bottomless and topless supporting jacket, to texture only the sidewalls in order to achieve the above-mentioned advantages andimprovements over smooth-surface or smooth-walled light-weight plasticbottles. It is of advantage in the absence of a cardboard jacket totexture to depths of 0.05 to 0.15 mm those parts of the bottle wallwhich are formed by application to a blow molding surface prepared inits entirety by etching, profile milling or erosion.

It is also possible to produce various surface textures, which enablevarious parts of the bottle wall to be differently textured, by etchingcertain portions of the molding surfaces of the bottle blowing molds andsand-blasting other portions thereof. Basically, portions of the moldingsurfaces of the bottle blowing molds may be prepared by differenttexturing methods. The entire molding surface of a bottle blowing moldmay thus be locally textured by application of one of the methodsmentioned above. In other words, the roughness is produced by acombination of two or more of the methods mentioned above. Thecombination of various texturing methods also influences the strength ofthe plastic bottle produced. Thus, those parts of the bottle blowingmold which form the shoulder of the bottle may be sandblasted whilethose parts which form the body and base of the bottle may be etched.

Known bottle blowing machines and blow molds may be used for theproduction of the thin-walled blow-molded plastic bottles with anoverall wall thickness of 0.1 to 0.3 mm, of which the walls are locallytextured to depths of 0.05 to 0.15 mm. The molding surfaces of thebottle blowing molds are prepared by etching, profile milling, sandblasting and erosion. The bottles are then blown as in standard bottleblowing processes. For the plastic bottles according to the invention,the bottle blowing compound is used in a quantity of, for example, 24±1g or less for a 1-liter PE bottle. Those parts of the bottle blowingmolds to which the bottle compound is applied during blow molding toform the wall zones of the plastic bottle textured in accordance withthe invention are prepared by etching, profile milling or erosion insuch a way that, after the bottle compound has been blow-molded to formthin-walled plastic bottles with overall wall thicknesses of 0.1 to 0.3mm, these zones of the plastic bottle have depths of 0.05 to 0.15 mm.The texture is so deep that it also appears on the inside of the bottle.The plastic bottles with walls textured in accordance with the inventionmay have any of the cross-sectional forms typical of standardblow-molded plastic bottles, i.e. they may have round, polygonal orsimilar cross-sections. It is preferred that the walls have a triangularor polygonal or trapezoidal cross-section where they are surrounded by abottomless and topless supporting jacket.

BRIEF DESCRIPTION OF THE DRAWING

The invention is described in more detail in the following withreference to the accompanying drawing, which is a schematic section onan enlarged scale through part of the wall of a thin-walled blow-moldedplastic bottle of polyethylene (PE).

DETAILED DESCRIPTION OF THE INVENTION

The plastic bottle is preferably surrounded by a bottomless and toplesssupporting jacket (not shown). The plastic bottle, including the walldetail shown in the drawing, has an overall wall thickness 1 of 0.1 to0.3 mm. The wall is textured both on its outer surface 2 and on itsinner surface 3. The texture formed on the outer surface 2 and on theinner surface 3 has depths 4, 5 of 0.05 to 0.15 mm. The texture isproduced by application of the outer surface 2 to blow mold surfacesprepared by etching, profile milling or erosion during the blow moldingof the plastic bottle. In this production process, the texture producedon the outer surface 2 of the wall by the prepared blow mold surfaces isalso reproduced on the inner surface 3 of the wall, i.e. on the insideof the plastic bottle. Although this does not increase the actual wallthickness 6 of the plastic bottle, it does increase the wall thickness 1relative to the actual wall thickness 6 because the distance between theouter surface 2 and the inner surface 3 is greater because of thetexture.

Although various embodiments of the present invention have been shownand described herein, they are not meant to be limiting. Those of skillin the art may recognize certain modifications to these embodiments,which modifications are meant to be covered by the spirit and scope ofthe appended claims.

What is claimed is:
 1. A thin-walled, blow-molded plastic bottle with avery thin overall wall thickness of 0.1 to 0.3 mm, and said bottlehaving a polygonal cross-section, wherein at least inner and outer sidewall portions of said bottle are textured to have a roughened surfacethat is uneven to depths of 0.05 to 0.15 mm.
 2. The blow-molded plasticbottle of claim 1, wherein said bottle consists of one of a family ofplastics including polyethylene (PE), polypropylene (PP), andpolyethylene terephthalate (PET).
 3. The blow-molded plastic bottle ofclaim 1, wherein the side wall portions of said bottle are textured onboth inner and outer surfaces thereof.